1. Field of the Invention
The invention relates to a profile of a rotor blade of a wind power plant, a plurality of such profiles and a corresponding rotor blade of a wind power plant.
2. Description of Related Art
The document DE 10 2008 003 411 A1 discloses a corresponding profile of a rotor blade of a wind power plant and a corresponding family or a plurality of profiles. The airfoils, or respectively profiles, disclosed in this document have an obtuse trailing edge, a substantially oval suction side, and a substantially S-shaped pressure side.
Further profiles are also known. In particular, low speed profiles are also known which are used in the proximity of the blade root, or in the proximity of the hub, of a wind power plant.
From “Niedriggeschwindigkeitsprofile” (“Low Speed Profiles”) by Dieter Althaus, Friedrich Vieweg & Sohn Verlagsgesellschaft mbH, Brauschweig/Wiesbaden, Germany, 1996, a known profile having lower relative thickness is produced in that a known profile is attained by cutting the trailing edge or scaling up the thickness to the required relative thickness values, which is necessary in the proximity of the blade root. The FX 77-W-500, shown on pages 162 and 163 in this book, can be cited as an example of this. This profile attains a maximum lift coefficient of ca=1.6 at an angle of attack of 10° in the clean state at a Reynold's number of 2.75 million, and in the unclean, thus turbulent, state attains a maximum ca of 0.8 at an angle of attack of 4°. The FX 77-W-500 has a relative profile thickness of 50%.
The angle of attack or angle of incidence is understood within the context of the invention to be an angle of the incoming apparent wind with respect to the chord of the profile. The textbook “Windkraftanlagen” (“Wind Turbines”) by Erich Hau, 4th Edition, 2008, particularly pages 126 ff, is referenced for any definitions.
Known profiles having a high relative profile thickness, for instance FX 77-W-500, have, in the clean state, an acceptable lift coefficient ca, however the maximum lift coefficient drops significantly during turbulent flows, that is in the unclean state. Also, the aerodynamic angle of attack, at which the maximum lift coefficient is attained in the unclean state, changes significantly. This behavior, namely the low lift in the case of fouling with a large change in the angle of attack for the maximum lift coefficient is very disadvantageous for wind power plants. If the angle used in the design of the rotor blade with the calculation of the respective profile is the angle, or a slightly smaller angle, at which the clean profile has the maximum lift coefficient, is selected as a design angle of attack, thus the angle of attack, which is expedient, as the blade depths should be kept low, then the lift coefficient in the unclean state reduces to a fraction of the clean value. The profile of the FX 83-W-500, due to the thick trailing edge, has already only moderate aerodynamic properties during laminar flow. With turbulent flow, it still has a high lift coefficient, but then has relatively poor drag ratios. Furthermore, the maximum thickness of this profile occurs at approximately 80% of the profile length or chord length, which is structurally less beneficial for a good body contour of the rotor blade. Thus, with a blade having the profile of the FX 83-W-500 only a relatively small distance of the main belts can be produced which causes corresponding disadvantages with the constructibility and the blade weight of a rotor blade.